1. Field of the Invention
The present invention relates to a lithium ion secondary battery system and a method for operating the lithium ion secondary battery system.
2. Description of the Prior Art
In recent years, with growing environmental problem concerns, developments of an electric automobile or a hybrid automobile are actively carried out. Accompanied with this, developments of a medium power battery of about 100 W to 1000 W used for the electric automobile or the hybrid automobile or the like, or a high power battery to be not less than 1000 W are advanced. As a battery for the automobile, although a large-sized battery by combining a large amount of the lead-acid batteries or the nickel-hydrogen batteries is mainly utilized, such battery has the problem that energy density per weight is low, and energy density per volume is low. For that reason, it is desired that the lithium ion secondly battery, which shows more excellent characteristics in an output or a heating or the like, may be made to apply to such automobile.
Conventionally, in the lithium ion secondary battery using the metallic lithium for a negative electrode, when carrying out quickly charging, lithium is extracted as dendrite to be crystalline state of acicular and/or dendritic, with the result that there is the problem of bringing about short circuit between the positive electrode and the negative electrode. In order to solve such the problem, there is disclosed the technique capable of repeatedly charging without producing charging failure while preventing growth of dendrite, upon charging with pulse current manner of repeatedly executing power feeding and pausing (Patent Literature 1).
On the other hand, in order to solve such the problem caused by the dendrite growth, the lithium secondary battery, which uses carbon material for a negative electrode, has been developed. However, in such a lithium ion secondary battery, there is the problem of occurring capacity loss at an initial charging caused by irreversibility of the carbon material. In order to solve such the problem, there is disclosed a technique to improve battery capacity, upon causing the battery to overcharge with small current at the time of initial charging (Patent Literature 2).
Further, conventionally, even though when the charge-discharge current of the lithium type rechargeable battery is small, in order to prevent disappearance of a passivation film formed in the vicinity of a lithium positive electrode, there is disclosed a technique, which intermittently uses the current (for instance, not less than C/2, when nominal capacity of the battery is taken to as C) larger than necessary charge-discharge current (Patent Literature 3).    Patent Literature 1: Japanese Laid-Open Patent Publication No. H06-36803    Patent Literature 2: Japanese Patent No. 2949705    Patent Literature 3: Japanese Laid-Open Patent Publication No. 564-77432    Patent Literature 4: Japanese Laid-Open Patent Publication No. 2002-260673 (TABLE 3, Comparison example 3)